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Dr Smart said after he received a message from Mr Halesworth: "I went downstairs and was shouting at my older son, 'Max, Max, I've found him' and he went straight on Facebook, Instagram and Snapchat - all those things teenage boys do - and told his mates."

Pharmaceutical scientist Dr Smart said he and Max arrived in the Spanish city last Saturday lunchtime and were on the underground to the match when he noticed his "wallet had taken leave from my pocket".

He found himself without any cards and unsuccessfully tried some shops to get cash via an online bank transfer to ensure they could get back to their hotel - a 10-mile (17km) walk away.

Dr Smart only had €3 (£2.59) when Mr Halesworth gave him money to "buy your son a hot dog, buy him a Coke and just enjoy yourself".

"I really wanted people to acknowledge and recognise something nice in the world," Dr Smart said of his appeal to find his helping hand.

"You forget about the nice things and here's someone who's done a nice thing and deserves some recognition."

Dr Smart has now donated the equivalent money to a charity called - The Kawasaki Kid, which helps people with the rare Kawasaki disease.

Mr Halesworth said it was "nice to hear everything was OK in the end" and said his charity donation was "a nice touch".